The following invention relates to apparatus which, in use, is located within the sea for the generation of electrical power from the motion of waves.
A number of devices have been tried and tested for this purpose, using the buoyancy of floats as a means of extracting energy, but as yet, none have proved to be of practical or economic use, or feasible in the long term. The efficacy of wave power generators, in common with all technological innovations, is determined by capital cost, the likely returns and reliability of operation. Of the three of these parameters, that which must be achieved first within the context of apparatus situated within the inhospitable and destructive environment of the oceans, is reliability.
Unless wave power apparatus can be made to function reliably and without risk of destruction over a reasonable period of time, consideration of the parameters of cost and return remains largely academic.
Of the various sea borne devices made to date, several do operate successfully to generate, experimentally, electrical power from the motion of waves. Examples of these are the hinged raft invented and developed by Sir Christopher Cockerell, and the bobbing duck invented and developed by Professor Steven Salter. There are several other such devices. These commonly operate by the use of buoyancy chambers, and the conversion of the undulating motion imparted thereto by sea waves into electrical power. Typical examples of conversion means are the use of gear chains, or hydraulic pumps, to turn rotary electrical generators.
These devices are, naturally, designed to operate effectively in xe2x80x98averagexe2x80x99 sea conditions, that is, taking into account the probable normal wave duration, height, and energy.
Unfortunately, although maybe only several times a year, wild storms do occur, and during these, the kinetic energy imparted by sea waves to any structure or device they encounter can be two orders of magnitude greater than that for which the devices had been originally been designed.
In these conditions, terminal damage may and does occur to mechanical devices exposed to the full force of the storm, with commensurate down time and crippling costs of repair. Solving the problem of designing apparatus that can withstand these crippling costs of repair. Solving the problem of designing apparatus that can withstand these occasional onslaughts and at a reasonable capital cost, is essential for the viability of any form of wave power generating apparatus.
In a co-pending application of the applicant, entitled Sea Wave to Electrical Energy Conversion Plant and filed at the UK Patent Office on Jul. 16, 1999 as application no. 9916779.3, machinery is disclosed for converting the energy of sea waves directly to electrical power, by means of the use of a float immersed within the sea waves to cause relative movement between the armature and stator of a linear generator, and in particular, a linear generator being a linear motor used in reverse and of a tubular construction.
In the invention of this co-pending application, because a linear generator is employed, electricity is generated without any need for linear to rotary motion conversion means, as has been the case with the other devices mentioned above. Power station means are furthermore described in that application, in which multiple generating units are contained safely within a tower mounted above the sea waves, and motion of the float of each unit is imparted respectively to each linear generator by a rigid mechanical connection means, for example, a cylindrical tube, or the like.
EP-A-0496146 discloses an apparatus for the generation of electrical power from the motion of sea waves comprising: a) at least one linear generator comprising an armature, a stator and a float, the apparatus having a first state in which normal, generating, operation occurs, in which the float is immersed in the sea for driving the armature of the linear generator in a linear reciprocating motion relative to the stator to generate electrical power; b) detection means for detecting the onset or occurrence of sea conditions unfavourable to the operation or survival of the at least one generator; and c) control means, responsive to the detection means to place the apparatus in a second state in which the float is caused to be wholly or partially submerged, to an extent sufficient to avoid any significant damage to the generator.
The invention seeks to provide an improved form of such apparatus.
According to the present invention, there is provided apparatus for the generation of electrical power from the motion of sea waves comprising:
a) at least one linear generator comprising an armature, a stator and a float, the apparatus having a first state in which normal, generating, operation occurs, in which the float is immersed in the sea for driving the armature of the linear generator in a linear reciprocating motion relative to the stator to generate electrical power;
b) detection means for detecting the onset or occurrence of sea conditions unfavourable to the operation or survival of the at least one generator; and
c) control means, responsive to the detection means to place the apparatus in a second state in which the float is caused to be held substantially or completely clear of the sea or to be wholly or partially submerged, in either case an extent sufficient to avoid any significant damage to the generator; and wherein
d) the control means (19) are adapted to reverse the mode of operation of the linear generator to that of a linear motor, the float (15) being driven to where it is held in the second state at least partly under the action of the linear generator acting as a linear motor.
Other, optional, features of the invention are defined in the sub-claims.
Thus, by the means of this invention, ie reversing the mode of operation of the linear generator,xe2x80x94which may be effected by supplying appropriately commutated currents thereto by batteries, or even by the reverse flow of current from the grid that it is normally supplying, it thereby becomes a motor for the extraction or submersion of the vulnerable part of the apparatus away from the worst excesses of the sea, until such time as the unfavourable conditions have abated. At that time, the motor is then operated to restore the float to the waves, and once safely ensconced, normal operation is resumed again as a generator. This invention may clearly be applied to the case in which the generating apparatus is supported in a tower above sea level, (as described in the co-pending application), or to an alternative case where the generating apparatus is contained within a tower which itself is submerged.
Because of its dual function, the full benefit of using linear generating means as a power source thus becomes apparent, in contrast to previous devices where their operative components remain permanently within the sea, and cannot be conveniently removed in the event of a storm by reversal of their operation from generator to motor.
In a feature of a first arrangement of this invention, namely that in which, in the second state, the linear generator, acting as a motor, is used to lift the float above the waves, a rugged protection chamber is provided into which the float can fit at an upper point in its travel. To overcome the waste of energy necessary to maintain the floatxe2x80x94by means of the linear motorxe2x80x94against gravity in its elevated position above the sea, a mechanical latch is provided to lock the float within its elevated position.
In a feature of the alternative arrangement of the invention, in which, in the second state, the float is submerged either partially, or completely below the worst excesses of the waves, thereby removing the need for any protection chamber as just described, the flotation chamber of the float is equipped with a valve, operable by the control means of the invention, for enabling flooding of the float to assist with its submersion. A secondary advantage of this arrangement is avoiding the waste of energy which would be need to power the linear generator, acting as a linear motor, to force and maintain the float in its submersed state.
Again, upon abatement of the storm, the float may be caused by the linear generator, acting as a linear motor, to emerge form the sea, with the flooding valve left open to enable water to drain from the float, and then to be closed for resuming normal operation of the device as a generator.
In an embodiment of this feature of the invention, a subsidiary hermetically sealed generator is enclosed within the float itself, operable by the motion of the float within the sea. The power generated thereby is used for two purposes, one being for the operation of a hazard warning lamp on the float, and the other, for supplying the electrical power necessary for operation of the flooding valve of the float. (A battery may be included as a storage means for the power thus generated.) Radio control means are further used to transmit from the control means of the invention, open/close signals to receptive control electronics housed within the float for operation, in turn, of the flooding valve. Thus the need for any electrical connection to the float is obviated, with commensurate advantages of simplicity and reliability.
According to a further, optional, feature of the invention, the aforementioned detection means used for determining whether to remove the float from the worst excesses of the sea waves, obtains its information from apparatus responsive to the relative motion of the stator and armature of the linear generator itself. This thereby directly provides information as to the aggressiveness of the motion of the sea waves. Compared with a pre-established wave motion data base, or other specific reference information, the information so gained is provided to the generator control means to automatically cause extraction/submersion of the float at an appropriate point, ie before wave motion becomes dangerously violent.
In yet a further feature related to this aspect of the invention, sea behaviour monitoring apparatus external to the wave power generating apparatus, is used instead of or in combination with the previously described means, to detect the onset or growth of storm conditions, and then to provide the necessary safety signal to the float extraction/submersion control means. Such apparatus may be, for example, one or more remote detector probes located in the sea well away from the generating apparatusxe2x80x94so providing sufficient time for its self protection as herein describedxe2x80x94or even the use of satellite or weather forecasting information.